Pediments and Cold-Climate Conditions, Barn Mountains, Unglaciated Northern Yukon, Canada

ABSTRACT

Pediments in the Barn Mountains constitute lowlands which border upland massifs and surround isolated inselberg-like hills. They form gentle concave-up or planar slopes which terminate abruptly at steeper upper slopes. Field observations demonstrate that the surfaces truncate geological structure and are essentially slopes of transportation since they possess a negligible or thin (<2-5 m thick) veneer of locally-derived colluvium. A study of the soils and surficial materials upon one pediment in Anker Creek (lat: 68°37'N; long: 138°08'W) suggests that the pediments are largely inactive under today's climate. Current geomorphic activity appears largely limited to the formation and movement of earth hummocks in the seasonally thawed layer. The pediments are probably old landform features which have been re-activated episodically only during those periods of the Pleistocene when enhanced moisture levels promoted intense frost wedging of upper slopes and permitted enhanced debris waste transport (solifluction) across the pediment. The initial mechanism of pediment formation is still unclear.